here - OSTA - Optical Storage Technology Association

3.2 Part 3 - Volume Structure
3.2.1 Logical Volume Header Descriptor
struct LogicalVolumeHeaderDesc { /* ECMA 167 4/14.15 */
Uint64 UniqueID,
bytes
reserved[24]
}
This structure is in the LVID Logical Volume Contents Use field.
3.2.1.1 Uint64 UniqueID
This field contains the next Next UniqueID value that should to be used. for the
next new objects in the UDF UniqueID Mapping Data Stream, see 3.3.7.1. The
field Next UniqueID value is initialized to 16, because the value 0 is reserved for
the root directory and itsystem stream directory objects and the values 1-15 are
reserved for use in Macintosh implementations. The Next UniqueID value
monotonically increases with each assignment of a new UDF UniqueID value for
a newly created object as described below. Whenever the lower 32-bits of this the
Next UniqueID value reach #FFFFFFFF, the next increment is performed by
incrementing the upper 32-bits are incremented by 1, as would be expected for a
64-bit value, but the lower 32-bits “wrap” to 16 (the initialization value). This
behavior supports Mac OS which uses an ID number space of 16 through 2 31 - 1
inclusive, and will not cause problems for other platformsAfter such a “wrap”, the
uniqueness of a 32-bits FID UDF UniqueID value can no longer be guaranteed.
Therefore the UDF UniqueID Mapping Data Stream shall be removed altogether
if the value of Next UniqueID is higher than #FFFFFFFF.
UniqueID is used whenever a new file or directory is created, or another name is
linked to an existing file or directory. During a rename or move operation, the FID
UniqueID value of an object shall not be changed and the values in the
corresponding UDF Unique ID Mapping Entry shall remain consistent, see
3.3.7.1.2. The parent references of this mapping entry shall be updated when an
object is moved to a different directory. When a FID is deleted, the mapping entry
corresponding to the now unused UDF Unique ID shall not be re-used but be
deleted or marked invalid. The File Identifier Descriptors and File
Entries/Extended File Entries used for a stream directory and named streams
associated with a file or directory do not use UniqueID; rather, the unique ID
fields in these structures take their value from the UniqueID of the File
Entry/Extended File Entry of the file/directory they are associated with. The same
counts for File Entries/Extended File Entries used to define an Extended
Attributes Space. A parent FID takes its Unique ID value from the 32 lower bits
of the File Entry/Extended File Entry that is identified by the parent FID.
FIDs and File Entries of the System Stream Directory and of streams associated
with the System Stream Directory shall use a UniqueID value of zero.
When a file or directory is created, this UniqueID is assigned to the UniqueID
field of the File Entry/Extended File Entry, the lower 32-bits of UniqueID are
UDF 2.01
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